The present invention relates to an ignition system of an internal combustion engine and, more particularly, to an ignition system of an internal combustion engine which uses a one-chip integrated circuit.
A prior art ignition system, as disclosed in Japanese Patent Laid-Open No. Sho 64-45963 (1989), has a self-shut-off function to detect trouble from the duration of a primary current, thereby forcibly opening the circuit. The function is to count the set time by a timer and to shut off the primary current when a condition has exceeded a preset period of time.
The above-described prior art pertains to a method of detecting trouble from the duration of the primary current, and needs a timer circuit. The use of the timer circuit will make the ignition circuit complicated, which will need a large-capacity capacitor for setting the time constant, presenting such a problem that only one chip is not enough for forming the ignition system.
This method is ineffective and not necessarily reliable against rupture of power transistors caused by sudden heating by a load dump surge arising in case of battery line trouble. Furthermore, there arises such trouble that re-energizing will occur during the ON state of an ignition control signal.
Furthermore, there arises such trouble that since a negative terminal for the ignition control signal of the ignition circuit is used in common with a GND terminal, the electric potential at a positive terminal of the ignition control signal varies from the reference GND with a current variation in the power system, making it impossible to detect a disconnection or short circuit at the positive terminal of the ignition control signal.